Saudi and British scientists, reporting in a daily, looked at symptoms and disease progression among 47 people, 36 of them men, admitted to Saudi hospitals with Middle East Respiratory Syndrome (MERS).

The vast majority of the patients had fever, coughing and shortness of breath, and minority experienced diarrhoea, vomiting and other gastrointestinal symptoms.

Such characteristics are shared with MERS' coronavirus cousin, Severe Acute Respiratory Syndrome (SARS), which triggered a global health scare a decade ago, they wrote. The two viruses also have the same incubation period.

But, according to the investigators, there are important differences between the two viruses. Unlike SARS, MERS is likelier to cause a fast-track progression to respiratory failure, taking five days less than SARS.

In addition, SARS affected people were relatively healthy and young, whereas MERS seems to target older patients and those with a chronic medical condition.

Out of the 47 cases, 45 were already being treated for diabetes, high blood pressure, heart or kidney disease and other disorders, according to the new study.

Statistically, MERS also appears to be deadlier. Twenty-eight out of the 47 patients died, a case-fatality rate of 60 percent, compared with only 1-2 percent for SARS.

"This high mortality rate with MERS is probably spurious due to the fact that we are only picking up severe cases and missing a significant number of milder or asymptomatic cases," cautioned Professor Ziad Memish, Saudi Arabia's deputy health minister, who led the research.

The kingdom accounts for 38 of the 45 fatalities recorded in nine countries, and 67 of the total 90 cases. Other cases have been recorded in Jordan, Qatar, the United Arab Emirates, Tunisia, Britain, France and Italy.

Key aspects of the virus, notably how it spreads and whether it has a reservoir among wild animals, remain unclear.